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From: rfrost@spam.ua.oz.au (Richard Frost)
Newsgroups: comp.sys.ibm.pc.programmer
Subject: Bug in TC2.0
Message-ID: <RFROST.90Jun3234439@spam.ua.oz.au>
Date: 3 Jun 90 14:14:39 GMT
Sender: news@ucs.adelaide.edu.au
Distribution: comp.sys.ibm.pc.programmer
Organization: Dept. of Stats Pure & Appl. Maths, Adelaide University
Lines: 61
X-Local-Date: 3 Jun 90 07:14:39 PDT


I have found what I think is a bug in version 2.0 of the Turbo C compiler.

I am a K&R C programmer from some time back and have not read the full specs
on ANSI C so I may be wrong.

Bug Description:
================

Consider 2 separately compiled C modules "A.c" and "B.c" which share an
array which is altered by a function in "B.c".

The 2 modules look like:

A.c:					B.c:
====					====

extern void testfn(void);

char Test[] = {0xB0,0xB0,0xB0};		extern char *Test;

main(int argc, char *argv[])		void testfn(void)
{					{
 ...					 ...
 testfn();
			 	 	 Test[1]  = 'A';
			 		 *(Test+2) = 'B';

}					}

When testfn() is called in main() it returns without altering
the array Test, however if the external reference to the array
in B.c is written as "extern char Test[]" then the function
succeeds in altering the array Test.

After looking at the assembly code produced, if the orignal external
reference is used when the code "Test[1]='A';" is executed, TC produces
code which dereferences Test as though it is a pointer to 
a pointer to char thus giving the address 0xB0B0 (which are the chars
in the initialized array) and then adding 1 and assigning to that address.

(Note: incorrect code is also produced for the other array access :
  *(Test+1) = 'B'; )

Correct assembly is produced when the other external reference is used,
ie "extern char Test[];" when the array is accessed in both manners shown.

I would like to know if this is really a bug, I think it IS according to K&R
rules.

Has anyone else had similar problems?.

--
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